Plasticizers, as polymer additives, are established main line additives and have been known for more than a century. Most high volume plasticizers have been developed in the last seventy years, primarily for use with vinyl and other polymeric substances. Significant volumes are sold, and plasticizers are used more than any other type of polymer additives, particularly in polyvinyl chloride (PVC) applications. PVC can be formulated into a tremendous number of products and is useful in innumerable applications. Plasticizers provide versatility to PVC and are key ingredients and tools for the vinyl formulator. They are used to adjust hardness (or softness), impart stain resistance, alter tensile properties (such as strength, elongation or flexibility) and processability as required for a multitude of applications, including without limitation flexible vinyl applications. While hundreds of plasticizers have been produced, only a few remain having acceptable performance properties when combined with vinyl or other polymeric materials.
There are a number of different types of plasticizers: 1) general purpose, 2) specialty types (such as high solvators), and 3) secondary types (oils) and diluent types (isodecyl benzoate, for example). Plasticizer additives are available in a wide variety of alternative chemistries.
In addition to chemistry type, plasticizers are categorized and distinguished based on their ability to solvate dispersed solid polymers and/or their gelation and fusion temperatures in plastisols. Gelation and fusion temperatures dictate the speed of production and are influenced by the solvating power of the plasticizer. By way of example, the gelation and fusion temperatures of a plastisol containing a dibenzoate plasticizer will be lower than a plastisol containing a general purpose phthalate, thus enabling speed of processing in that particular application.
Plasticizers serve as a vehicle for the dispersion of resin (polymer) particles, such as PVC. The dispersion is initially a two-phase, heterogeneous system. Use of plasticizers in polymeric dispersions promotes the formation of homogeneous systems and polymer fusion occurs upon heating. The higher the solvating power, the lower the temperature at which a homogeneous system is fused, which, in turn, decreases the residence time and increases the speed at which polymeric compositions can be processed into an end product, resulting in a faster, more efficient and economical process.
General Purpose Plasticizers.
General purpose plasticizers provide an excellent compromise between performance characteristics and economy for most applications. Some examples include: bis (2-ethylhexyl phthalate) (DEHP or DOP), diisononyl phthalate (DINP), dioctyl phthalate (DNOP), diisodecyl phthalate (DIDP), dipropylheptyl phthalate (DPHP), di-2-ethylhexyl terephthalate (DOTP or DEHT), and diisononyl-1, 2 cyclohexane dicarboxylate (DIDC or DINCH®) (as described in U.S. Pat. No. 7,855,340). General purpose phthalates dominate the volume of plasticizers purchased every year and are most often selected for compounding flexible vinyl.
Yearly, plasticizer production is in the area of 12 billion pounds, and the general purpose phthalate DOP accounts for about half of the pounds of plasticizer consumed, despite pressure from health and environmental issues encountered with the use of general purpose phthalates.
In view of the ongoing scrutiny of phthalate use, a need has developed for phthalate alternatives. Both DOTP and DIDC are contenders for phthalate replacement in the general purpose market. These two plasticizers are considered “next generation”, general purpose “non-phthalate” plasticizers. Even though DOTP, chemically, is a phthalate, it is not an orthophthalate, the use of which is subject to increasing regulatory pressure. These “next generation” phthalate alternatives are viable; however, they do not always give the performance desired in vinyl compositions, particularly in plastisols (i.e., they have poorer compatibility, slow speed, high gel temperatures, low gel strength). Blends of plasticizers can be used to adjust performance, although there may be some limits to this approach.
In addition to DOTP and DIDC, sustainable, “green” types of plasticizers are also contending for the general purpose plasticizer market. Examples include plasticizers based on castor oil and soybean oil.
Some applications, however, require performance that cannot be achieved by use of a general purpose plasticizer alone. Applications that require better resistance to oils and solvents are one such example. General purpose phthalates are easily extracted by nonpolar solvents such as hexanes, such that alternative plasticizers would be a much better choice. There is also a need for plasticizers that are higher solvators for PVC and other polymer applications.
Specialty-Type Plasticizers.
Specialty type plasticizers have been developed to fulfill the need for high solvators, the most popular being lower molecular weight phthalates. An example of such a plasticizer is butyl benzyl phthalate (BBP), which is often employed as a high solvating plasticizer. Di-n-butyl phthalate (DBP) and diisobutyl phthalate (DIBP) are also useful high solvator, specialty type plasticizers. Other examples of non-phthalate, high solvating plasticizers include some citric acid esters, alkyl sulfonic acid esters, and certain phosphates. Dibutyl terephthalate (DBTP) and N-alkyl pyrrolidones have also been proposed as a specialty type, high solvator plasticizers.
All of the high solvator plasticizers (regardless of type) add value to vinyl compositions that traditional general purpose plasticizers cannot. Even so, many of the high solvator plasticizers are phthalates, for which safer alternatives are being sought.
Benzoate Ester Plasticizers.
Benzoate ester plasticizers have also been developed as specialty type plasticizers. Benzoate plasticizers have been recognized since the 1940's as useful plasticizers for PVC applications, and subsequently some of these benzoate plasticizers were commercialized. Benzoate plasticizers are well established and have now been in use in PVC applications for decades. By their nature, benzoate plasticizers are non-phthalates; however, they were not created nor specifically established on that basis and were in use well before the demand for phthalate alternatives began. Benzoate plasticizers include monobenzoates and dibenzoates, among others.
Monobenzoate esters useful as plasticizers include: isodecyl benzoate, isononyl benzoate, and 2-ethylhexyl benzoate. “Half ester” monobenzoates include dipropylene glycol monobenzoate and diethylene glycol monobenzoate, which are byproducts of the production of dibenzoates, but which, most of the time, are not objects of production. Monobenzoates are not generally noted for being high solvators, although they may be used in conjunction therewith. Monobenzoates are also not as useful as dibenzoate plasticizers, because they are less compatible than the corresponding dibenzoate with PVC. However, the half esters are compatible with emulsions polymers, such as acrylic and/or vinyl ester polymers.
Classically, dibenzoate plasticizers function well as high solvating plasticizers and are recognized today as some of the best high solvators for PVC applications. Historically, diethylene glycol dibenzoates (DEGDB) and dipropylene glycol dibenzoates (DPGDB) esters are well known and have been used in many applications in the past, including the vinyl industry. DEGDB is an excellent plasticizer, but due to its high freeze point, blends with DPGDB were also developed to capitalize on the utility and lower cost of DEGDB. Several years ago a blend of DEGDB, DPGDB and triethylene glycol dibenzoates (TEGDB) was introduced as a high solvating dibenzoate blend.
State of the Art
Benzoate ester plasticizers, alone or in a blend with other plasticizers, are commercially available and are described in the literature and in prior patents. Plastisol and organosol compositions, adhesives, caulks, polishes, inks, and a wide variety of coatings containing benzoate plasticizers are also known in the art.
By way of example, U.S. Pat. No. 4,950,702 to Arendt discloses plastisol compositions comprising a polyvinyl resin plasticized with dipropylene glycol monomethyl ether benzoate or tripropylene glycol monomethyl ether benzoate.
U.S. Pat. No. 5,236,987 to Arendt discloses the use of isodecyl benzoate as a coalescent agent for use in paint compositions and in the preparation of plastisols.
U.S. Pat. No. 5,319,028 to Nakamura et al. describes a plastisol composition that comprises PVC resin and a plasticizer used singly, or in combination, that may include, among other plasticizers, glycol derivatives, such as DEGDB, DPGDB, and TEG di-(2-ethylhexoate).
The use of dibenzoate esters alone or in combination with their corresponding monobenzoate ester is described in U.S. Pat. No. 5,676,742 to Arendt et al., which discloses plasticized aqueous polymer compositions useful as latex caulks.
Dibenzoate plasticizer blends used as the primary plasticizer for a plastisol composition are described in U.S. Pat. No. 5,990,214 to Arendt et al., which discloses blends comprising the dibenzoates of both DEG and triethylene glycol for use in plastisol applications.
U.S. Pat. No. 7,812,080 to Arendt et al. describes a plastisol having a dispersed phase and a liquid phase, the liquid phase including dibenzoate plasticizer blends having a hydroxyl number of about 30 or greater indicating a higher half ester monobenzoate content. The plastisols provided are stated to be effective for providing a foamed composition having an improved color.
U.S. Pat. No. 6,583,207 to Stanhope et al. describes the addition of at least about 30 wt. % of DEG or DPG half ester monobenzoates to DEG dibenzoate to form a liquid mixture at around 28° C. Similarly, U.S. Pat. No. 7,056,966 to Stanhope et al. describes the addition of at least 20 wt. % of at least one half ester monobenzoate to at least one dibenzoate to form a liquid mixture at around 28° C. These liquid mixtures are described as effective plasticizers for aqueous polymer compositions, such as adhesives and caulk.
U.S. Pat. No. 7,071,252 to Stanhope et al. describes the use of half ester monobenzoates as secondary plasticizers for non-aqueous and solvent-less plastisols containing primary plasticizers.
U.S. Pat. No. 7,872,063 to Strepka et al. describes a film-forming composition, such as a polish, coating, adhesive or ink, comprising at least one acrylic or vinyl acetate polymer as the film-forming component in combination with a plasticizer blend comprising an aromatic dibenzoate, DEGDB and DEGMB.
U.S. Pat. No. 7,629,413 to Godwin et al. describes a PVC plastisol composition comprising C9-C11 alkyl benzoates in combination with phthalate plasticizers to reduce viscosity and reduce staining problems associated with the phthalates.
U.S. Pat. No. 8,034,860 to Arendt et al. describes an organosol plastisol composition comprising plasticizers that are diesters of benzoic acid and dihydric alcohols in combination with an organic diluent. Monoesters of benzoic acid and monohydric alcohols are also described as auxiliary plasticizers.
U.S. Pat. Publication No. 2009/0036581 to Joshi et al. describes plasticizers for polymers based on blends of the mono- and di-benzoates of 2,2,4-trimethyl-1,3-pentanediol, containing a minimum of 87 weight percent of the dibenzoate, which can be used in combination with dipropylene glycol benzoates.
In sum, benzoate esters, including DPGDB and DEGDB blends, have been used in many applications. Dibenzoate plasticizers provide improved processability, fast fusion and stain resistance, among other properties that are favorable for many polymer applications.
The focus of the present invention is on non-phthalate, high solvator plasticizer compositions, since general purpose phthalate plasticizers—although widely used, effective and economical in vinyl—are not efficient solvators. Moreover, the use of phthalates has been under increased attack by governmental agencies due to environmental, health and safety issues associated with their use. And, while the specialty phthalate plasticizer butylbenzyl phthalate (BBP) was widely regarded as the holy grail of plasticizers in that it was an excellent (high) solvator with low viscosity and a desirable rheology profile, it, too, has now come into disfavor as a potential teratogen and toxin.
Accordingly, there continues to be a need for alternatives to currently available high solvating phthalate plasticizers and, hence, benzoate plasticizers and blends thereof are viable alternatives due to their high solvating properties.
Of particular interest in the present invention are dibenzoate plasticizers, which, as discussed above, have been known and used for their high solvating properties in a variety of applications. Even so, dibenzoate use in plastisols may be limited by high plastisol viscosity and undesirable rheology over time as the plasticizer continues to solvate. As the plastisol composition ages, it is rendered more and more viscous. In addition, high solvator plasticizers may be less heat and UV light stable. They are also denser than general purpose plasticizers and have a higher migration than general purpose types when used in polymeric products, such as plastisols.
These limitations are described in the '860 to Arendt et al. mentioned above. The '860 patent describes a plastisol comprising a dispersed polymer and a DEG/DPG dibenzoate blend that resulted in a 25-fold increase in plastisol viscosity, which was far too viscous for processing using conventional equipment. The publication further discloses a plastisol composition comprising a dispersed polymer, dibenzoate plasticizers (among others) and an organic diluent (solvent), wherein viscosity increase was avoided or reduced by selecting and matching components based upon specific differences between a) the Hildebrand solubility parameter of the polymer and b) the weighted average of the Hildebrand solubility parameters of the organic diluent (solvent), plasticizers and any other liquid ingredients present in the plastisol. The difference between a and b is required to be within specified limits to avoid too high a plastisol viscosity on the one hand, or the possibility of exudation of liquids from articles formed from the plastisol on the other hand. The plasticizer was selected from the group consisting of diesters of benzoic acid and dihydric alcohols, such as propylene glycol, and oligomeric ether glycols, such as diethylene glycol, triethylene glycol, dipropylene glycol and 1,3-butanediol, as well as diesters of phthalic acid and monohydric alcohols.
In response to continued needs in the PVC industry, a new dibenzoate triblend platform has been developed which can been optimized for performance and handling in polymeric compositions, and which provides an improvement over some traditional benzoate plasticizers and blends, in particular with respect to plastisol rheology. The novel blend comprises three dibenzoate plasticizers that have surprisingly fewer viscosity limitations than would be expected based on the viscosities of the individual components. A blend of dibenzoate plasticizers, i.e., DEGDB and DPGDB in specified ratios, forms the base of the inventive plasticizer triblend in combination with 1,2-propylene glycol dibenzoates (PGDB). 1,2-Propylene glycol dibenzoate is a known component previously used alone with PVC or in plasticizer blends unrelated to the present inventive triblend. 1,2-Propylene glycol dibenzoate was, also known as a flavoring agent for beverages as described in U.S. Pat. No. 3,652,291 to Bedoukian.
The inventive triblend is useful as a high solvating plasticizer in plastisol applications and, unexpectedly, the combination provides lower viscosity and improved rheology characteristics in plastisols over what would be expected based on the rheological characteristics of each of the individual components of the triblend. The novel triblend is compatible and efficient when used in plastisol formulations and provides improved processability, whether used as a primary plasticizer or as a blending plasticizer in conjunction with poor solvating plasticizers. The novel triblend of DPGDB, DEGDB, and PGDB has not been utilized in the past.
The focus of the present invention is on the use of the inventive blend to formulate novel plastisol compositions for use in flooring applications. However, the invention is not limited to flooring applications. The inventive plasticizer triblend can be used individually and in blends with other plasticizers in applications that include but are not limited to: adhesives, caulks, architectural coatings, industrial coatings, OEM coatings, other types of plastisols, sealants, overprint varnishes, polishes, inks, melt compounded vinyl, polysulfides, polyurethanes, epoxies, styrenated acrylics and combinations thereof. Other applications will be evident to one skilled in the art based upon the disclosure herein.
Principle applications for the inventive triblend include:
PVC: the inventive triblend has been shown to be a high solvating plasticizer, with unexpectedly lower viscosity than what would be expected based upon the viscosities of the individual components.
Coatings: the inventive triblend has been shown to have utility in coating technology, primarily as a low VOC coalescent, that has excellent compatibility with the polymers utilized in the architectural and industrial coatings industry. This application is the subject of a co-pending application. The inventive triblend may also be used in other coatings and film-forming compositions, such as polishes, inks and overprint varnishes, among others.
Adhesives: the inventive triblend is highly compatible and has good viscosity response and Tg (glass transition temperature) suppression.
Sealants and Caulks.
It is an object of the invention to provide a non-phthalate plasticizer composition for use as a primary plasticizer or as a specialty plasticizer in polymeric compositions traditionally requiring plasticizers, including without limitation PVC applications.
It is another object of the invention to provide a non-phthalate plasticizer composition that is compatible with a wide range of polymeric compositions, has high solvating properties, and is useful as a specialty blending plasticizer to improve the compatibility and processability of poor solvating plasticizers.
It is yet another object of the invention to provide a non-phthalate plasticizer composition for use in plastisols, having high solvating properties, while minimizing the attendant disadvantages of high viscosity and poor rheology associated with the use of high solvators in plastisols.
It is a further object of the invention to provide a plastisol formulation utilizing a non-phthalate plasticizer, which allows faster processing and economic efficiencies to be achieved.
It is yet another object of the invention to provide a plastisol formulation utilizing a non-phthalate plasticizer, which provides higher tensile strength and stain and extraction resistance.
Still further objects of the invention are to provide an adhesive formulation and an overprint varnish utilizing the non-phthalate plasticizer triblend of the invention.
Other objects of the invention will be apparent from the description herein.